Known folders in rotary offset printing presses convert a continuous web of printed paper into a series of books or pamphlets folded according to various types of folds. These machines usually make two folds: the first fold is a cylinder fold or tabloid fold, and the second fold may be either a parallel fold or delta fold. The second fold is typically made so that point holes formed on the web appear on the inside of the final product. The web is generally already folded in half before entering the folder by a device called a former. The former continuously folds the web in the longitudinal direction so that a fold parallel to the edges of the web width is created.
Because of various customer demands, it is necessary that folders be able to make both second parallel folds and delta folds. Therefore, such folders must be able to assume two different configurations which are necessary for making both types of folds.
These folders are comprised of a cutting cylinder, a transfer cylinder, a first-fold cylinder, and a second-fold cylinder. The cutting cylinder has a cutting blade which engages with a cutting counterpart on the transfer cylinder for cutting the web into signatures. The transfer cylinder is equipped with pairs of spur bars and engaging blades which cooperate with first-fold jaws on the first-fold cylinder for forming a first fold in the signature. The first-fold cylinder is equipped with pairs of first-fold jaws and second fold jaws which cooperate with pairs of grippers and engaging blades disposed on the second-fold cylinder for forming a second fold in the signature.
The spacing between each of the respective pairs of elements of the respective cylinders determines the type of fold that is created. Therefore, in order to change the type of fold made, the spacing between the respective elements must be altered. This change can translate into angular displacements of between 10.degree. and 20.degree. to convert the folder from a configuration which forms second parallel folds to one that forms delta folds.
These angular displacements are far greater than the angular displacement that these cylinders are generally capable of when each of the cylinders is produced in two imbricated independent parts movable relative to one another and equipped with respective driving gears. In fact, such a form of construction is often employed to make it possible to adjust the lap length by introducing a slight angular offset (typically only a few degrees) between the respective driving gears, these gears moreover being coupled to one another two-by-two in order to preserve coincidence between the elements which must cooperate with one another during the passage of the paper web between two adjacent cylinders. To adjust the lap length, a single double-helical pinion is used which is driven by each respective pair of gears of the relevant cylinder during the normal operation of the folder. One portion of this pinion meshes with one of the gears, and the other portion meshes with the other gear. The operator effects a slight axial translational movement of this double.helical pinion, the axis of which remains parallel to that of the relevant Cylinder, thereby making it possible to obtain a slight angular displacement in the desired direction between the associated pair of gears. However, such a relative angular adjustment can only be used for displacements of a few degrees.
Therefore, this technique for adjusting the lap length is virtually impractical for the purpose of obtaining angular displacements of the magnitude of 10 to 20.degree.. To obtain angular displacements of 10 to 20.degree., a translational movement of a length ten to twenty times greater than that which the double.helical pinion is capable, may be necessary. Although that solution is theoretically possible, it is typically not used in practice, because the lateral bulk of the folder is considerably increased.
This explains why, in conventional folders, the removal of the various groups of elements on the relevant cylinders is carried out manually. In fact, an operator usually has to remove all the first-fold engaging blades from the transfer cylinder in order to readjust them in relation to the spur bars, all the second-fold jaws of the first-fold cylinder in order to readjust them in relation to the first-fold jaws, and all the second fold engaging blades of the second-fold cylinder in order to readjust them in relation to the grippers. These operations are complicated, involve the use of various tools and cause a rather lengthy operational shutdown of the press.
Various other solutions have also been proposed for modifying the configuration of a universal folder for the purpose of obtaining either a second parallel fold or a delta fold., For example, some use one or more specialized cylinders for the delta fold and other specialized cylinders for the second parallel fold. Although this may avoid the individual operations of removing and refitting the elements of these cylinders, it nevertheless still involves shutting down the machine and manually substituting the specialized Cylinders. This solution is incomplete, since operator intervention is still necessary, a relative long shut down is still required, and specialized cylinders are required.
Another proposed solution involves rotating the various parts of the cylinders by means of complex drives, e.g., "harmonic drives". However, this solution is costly and complex.
Therefore, all of these solutions are either difficult to put into practice, requiring manual intervention inside the machine, or are costly and complex.